This invention relates to the use of polyimidesiloxane membranes for separating a first fluid from a mixture with a second fluid.
There are many applications where it is desirable to increase or decrease the concentration of a particular fluid in a mixture of fluids. For example, if air is to be used as a source of oxygen in a combustion or other chemical process, it may be economical or otherwise desirable to use air that contains a higher than normal concentration of oxygen. In other processes, it may be desirable to use air that contains a higher concentration of nitrogen. In some industrial processes a mixture of fluids is produced which must be separated into the component fluids. For example, fermentation processes can produce a mixture of ethanol in water. Other processes can produce water containing pollutants such as benzene or chloroform, and these pollutants must be removed from the water before the water can be discharged or recycled.
One relatively economical way of separating two fluids is to place the mixed fluids in contact with a membrane that is more permeable to one of the fluids than to the other. Membranes that have been used for this purpose include polysulfones, polyethersulfones, cellulose acetate, polysiloxanes, and polyimides. The particular chemical composition of the membrane determines the permeability of a fluid to it. However, a complete understanding of the relationship between the chemical composition of the membrane and the permeability of particular fluids has not yet been achieved.